Methods for forming aerosol-generating substrates having a reduced amount of tobacco specific nitrosamines

ABSTRACT

There is provided a method of forming an aerosol-generating substrate, the method including providing a liquid nicotine source containing at least one tobacco-specific nitrosamine; mixing the liquid nicotine source with a solvent and at least one aerosol former to form an aerosol-generating substrate; and irradiating the aerosol-generating substrate with ultraviolet light to reduce an amount of the at least one tobacco-specific nitrosamine. Also provided is a method of forming an aerosol-generating substrate, the method including providing a tobacco slurry containing at least one tobacco-specific nitrosamine; irradiating the tobacco slurry with ultraviolet light to reduce an amount of the at least one tobacco-specific nitrosamine; and drying the tobacco slurry to form an aerosol-generating substrate.

The present invention relates to methods of forming aerosol-generating substrates having a reduced amount of tobacco-specific nitrosamines. The aerosol-generating substrates formed according to the present invention find particular application as substrates for electrical smoking systems.

Electrically operated smoking systems that vaporise a liquid nicotine formulation to form an aerosol that is inhaled by a user are known in the art. For example, a known electrically operated smoking system comprises a shell and a replaceable mouthpiece wherein the shell comprises an electric power supply and electric circuitry. The mouthpiece comprises a liquid storage portion, a capillary wick having a first end that extends into the liquid storage portion for contact with liquid therein, and a heating element for heating a second end of the capillary wick. In use, liquid is transferred from the liquid storage portion towards the heating element by capillary action in the wick. Liquid at the second end of the wick is vaporised by the heating element.

Electrically operated smoking systems that heat a tobacco product, such as a cast leaf tobacco product, are also known. For example, a known electrically operated smoking system comprises a resistively heated ceramic heater blade that is inserted into a tobacco rod to generate an aerosol comprising volatile compounds contained within the tobacco. Cast leaf tobacco products are formed by casting and drying a tobacco slurry.

Liquid nicotine formulations and tobacco slurries are typically derived from cured tobacco materials. As such, liquid nicotine formulations and heated tobacco products formed from tobacco slurries may be undesirably contaminated with tobacco-specific nitrosamines (TSNAs), such as N-nitrosonornicotine (NNN), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), N-nitrosoanatabine (NAT) and N-Nitrosoanabasine (NAB).

A known method for reducing TSNA contamination of nicotine purified from cured tobacco materials includes chemical treatment of the tobacco plants prior to harvest to increase antioxidant production and prevent TSNA formation during curing. However, the process of treating the tobacco plants is time consuming, costly, and care must be taken to prevent environmental contamination with the chemicals used.

It would therefore be desirable to provide a method of reducing or eliminating TSNA contamination of nicotine that overcomes these difficulties associated with known methods of TSNA reduction.

According to a first aspect, the present invention provides a method of forming an aerosol-generating substrate, the method comprising providing a liquid nicotine source containing at least one tobacco-specific nitrosamine, mixing the liquid nicotine source with a solvent and at least one aerosol former to form an aerosol-generating substrate, and irradiating the aerosol-generating substrate with ultraviolet light to reduce the amount of the at least one tobacco-specific nitrosamine.

As used herein, the term “aerosol-generating substrate” refers to a substrate capable of releasing volatile compounds, which can form an aerosol. The aerosols generated from aerosol-generating substrates according to the invention may be visible or invisible and may include vapours (for example, fine particles of substances, which are in a gaseous state, that are ordinarily liquid or solid at room temperature) as well as gases and liquid droplets of condensed vapours.

By using ultraviolet (UV) light to reduce the amount of one or more TSNAs in an aerosol-generating substrate containing a liquid nicotine source, the method according to the first aspect of the present invention advantageously eliminates the need for chemical removal processes. The method according to the first aspect of the present invention may therefore be cheaper, produce little or no waste, and minimise any health and environmental concerns when compared to existing processes. Furthermore, since the present invention utilises UV irradiation of an aerosol-generating substrate comprising a liquid nicotine source it can be applied to solutions of nicotine already separated from the tobacco plant material. This is in contrast to known methods, such as the chemical treatment method described above that requires treatment of the tobacco plant during cultivation and prior to harvest, and other known methods that attempt to reduce TSNA content by optimising the conditions under which the harvested tobacco is cured.

The solvent may comprise water or an organic solvent. Additionally, or alternatively, the at least one aerosol former may comprise at least one of propylene glycol and glycerin.

In any of the embodiments described above, the ultraviolet irradiance of the aerosol-generating substrate is preferably at least about 4 milliwatts per square centimetre, more preferably at least about 40 milliwatts per square centimetre, most preferably at least about 400 milliwatts per square centimetre. UV irradiance at or above these levels can provide significant reduction of the amount of the one or more TSNAs within a relatively short time period. The irradiation level of a fluid can be determined using a UV radiometer.

Additionally, or alternatively, the UV irradiance step preferably comprises irradiating the aerosol-generating substrate with ultraviolet light for less than about 180 minutes, more preferably less than about 120 minutes, yet more preferably less than about 60 minutes, most preferably less than about 30 minutes. Irradiating the aerosol-generating substrate with ultraviolet light for a period within these ranges can provide significant reduction in the amount of the one or more TSNAs. These time periods refer to the total duration of the UV irradiation and the total duration may be a single consecutive period of irradiance, or two or more discrete periods of irradiance. For example, in those embodiments in which the irradiating step comprises irradiating the aerosol-generating substrate with UV light for 30 minutes, the irradiance may be conducted in a single 30 minute step, or in two separate steps each of 15 minutes long.

Generally, increasing the UV irradiance will yield a higher reduction in TSNA content over a fixed time period. Therefore, to optimise the efficiency of the TSNA reduction process, a high UV irradiance is preferably used to minimise the total time required to reduce the TSNA content to a desired level. In any of the embodiments described above, the amount of the at least one tobacco-specific nitrosamine present in the aerosol-generating substrate after the irradiation step is preferably less than about 75 percent by weight of the amount of the at least one tobacco-specific nitrosamine present in the aerosol-generating substrate before the irradiation step, more preferably less than about 50 percent by weight of the amount of the at least one tobacco-specific nitrosamine present in the aerosol-generating substrate before the irradiation step, most preferably less than about 25 percent by weight of the amount of the at least one tobacco-specific nitrosamine present in the aerosol-generating substrate before the irradiation step. Generally, the reduction in the amount of the at least one tobacco-specific nitrosamine can be increased by increasing at least one of the irradiance and the duration of the irradiating step. For a given irradiance, the amount of the at least one tobacco-specific nitrosamine present in the aerosol-generating substrate decreases in a generally exponential manner during the period of irradiation.

According to a second aspect, the present invention provides a method of forming an aerosol-generating substrate, the method comprising providing a tobacco slurry containing at least one tobacco-specific nitrosamine, irradiating the tobacco slurry with ultraviolet light to reduce the amount of the at least one tobacco-specific nitrosamine, and drying the tobacco slurry to form an aerosol-generating substrate.

By using ultraviolet (UV) light to reduce the amount of one or more TSNAs in an aerosol-generating substrate formed from a tobacco slurry, the method according to the second aspect of present invention advantageously eliminates the need for chemical removal processes. The method according to the second aspect of the present invention may therefore be cheaper, produce little or no waste, and minimise any health and environmental concerns when compared to existing processes. Furthermore, since the present invention utilises UV irradiation of a tobacco slurry it can be applied to tobacco plant material that has already been harvested and processed. This is in contrast to known methods, such as the chemical treatment method described above that requires treatment of the tobacco plant during cultivation and prior to harvest, and other known methods that attempt to reduce TSNA content by optimising the conditions under which the harvested tobacco is cured.

The tobacco slurry may be cast and dried to form a cast leaf tobacco. In this case, the tobacco slurry may be irradiated before casting, after casting, or both. Such a method may be advantageous in that it would allow for integration of an apparatus capable of irradiating the slurry directly into a casting line.

As used herein, the term “cast leaf tobacco” refers to a homogenised tobacco material typically formed by casting a tobacco slurry comprising particulate tobacco and one or more binders onto a conveyor belt or other surface, drying the cast slurry to form a sheet of homogenised tobacco material and removing the sheet of homogenised tobacco material from the support surface.

In any of the embodiments described above, the ultraviolet irradiance of the tobacco slurry is preferably at least about 4 milliwatts per square centimetre, more preferably at least about 40 milliwatts per square centimetre, most preferably at least about 400 milliwatts per square centimetre. UV irradiance at or above these levels can provide significant reduction of the amount of the one or more TSNAs within a relatively short time period. The irradiation level of a fluid can be determined using a UV radiometer.

Additionally, or alternatively, the UV irradiance step preferably comprises irradiating the tobacco slurry with ultraviolet light for less than about 180 minutes, more preferably less than about 120 minutes, yet more preferably less than about 60 minutes, most preferably less than about 30 minutes. Irradiating the tobacco slurry with ultraviolet light for a period within these ranges can provide significant reduction in the amount of the one or more TSNAs. These time periods refer to the total duration of the UV irradiation and the total duration may be a single consecutive period of irradiance, or two or more discrete periods of irradiance. For example, in those embodiments in which the irradiating step comprises irradiating the tobacco slurry with UV light for 30 minutes, the irradiance may be conducted in a single 30 minute step, or in two separate steps each of 15 minutes long. The total irradiation time may be varied according to the thickness of the tobacco slurry. That is, the total irradiation time may be increased as the thickness of the tobacco slurry is increased.

Generally, increasing the UV irradiance will yield a higher reduction in TSNA content over a fixed time period. Therefore, to optimise the efficiency of the TSNA reduction process, a high UV irradiance is preferably used to minimise the total time required to reduce the TSNA content to a desired level. In any of the embodiments described above, the amount of the at least one tobacco-specific nitrosamine present in the tobacco slurry after the irradiation step is preferably less than about 75 percent by weight of the amount of the at least one tobacco-specific nitrosamine present in the tobacco slurry before the irradiation step, more preferably less than about 50 percent by weight of the amount of the at least one tobacco-specific nitrosamine present in the tobacco slurry before the irradiation step, most preferably less than about 25 percent by weight of the amount of the at least one tobacco-specific nitrosamine present in the tobacco slurry before the irradiation step. Generally, the reduction in the amount of the at least one tobacco-specific nitrosamine can be increased by increasing at least one of the irradiance and the duration of the irradiating step. For a given irradiance, the amount of the at least one tobacco-specific nitrosamine present in the tobacco slurry decreases in a generally exponential manner during the period of irradiation.

In any of the embodiments described above, in accordance with the first aspect or the second aspect of the present invention, the ultraviolet light used in the irradiating step preferably has a peak intensity at a wavelength of at least about 315 nanometres, more preferably at least about 335 nanometres, most preferably at least about 350 nanometres. Additionally, or alternatively, the ultraviolet light preferably has a peak intensity at a wavelength of less than about 400 nanometres, more preferably less than about 390 nanometres, most preferably less than about 380 nanometres. In particularly preferred embodiments, the ultraviolet light has a peak intensity at a wavelength of between about 315 nanometres and about 400 nanometres, more preferably between about 335 nanometres and about 390 nanometres, most preferably between about 350 nanometres and about 380 nanometres. The ultraviolet light may have a peak intensity at a wavelength of about 365 nanometres. UV light having a peak intensity at a wavelength within these ranges falls within the UV-A portion of the ultraviolet spectrum, which the present inventors have recognised provides effective reduction of TSNAs and is optimised for transmission through glass and common UV transparent polymeric packaging materials. Therefore, methods in accordance with these embodiments are particularly suited for the treatment of aerosol-generating substrates or tobacco slurries that are housed within a glass container, or housed within a container comprising a glass window through which the UV light is transmitted. Use of radiation having a shorter wavelength is undesirable, as it may result in undesirable chemical decomposition of the nicotine.

According to a third aspect, the present invention provides an aerosol-generating substrate formed using the method according to either the first aspect of the invention or the second aspect of the invention, in accordance with any of the embodiments described above.

EXAMPLE 1

Defined concentrations of N-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) (380 and 613 nanograms per millilitre, respectively) were added to three different liquid aerosol-generating substrates each consisting of nicotine, glycerin, propylene glycol and water (2:10:68:20, 2:39:39:20 and 2:68:10:20 by weight). Aliquots of these solutions were placed in clear glass vials and irradiated for a specified time (0, 15, 30, 60, 120 or 240 minutes) with ultraviolet radiation (wavelength of 365 nanometres; lamp nominal power of 8 watts; distance to lamp of 3 centimetres). After irradiation the samples were diluted ten-fold with water and their nicotine, NNN and NNK content was analyzed.

The UV irradiation caused a time-dependent decrease of NNK and NNN in all three nicotine/glycerin/propylene-glycol/water mixtures. Nicotine concentrations were not affected. The nitrosamine decay is approximately exponential with respect to irradiation time. Half-lives for NNN and NNK were in the ranges of 30-50 minutes and 60-70 minutes, respectively. The results are illustrated in FIGS. 1 to 3.

EXAMPLE 2

A sample sheet of cast tobacco slurry having a thickness of 0.20 to 0.22 millimetres after drying to 195 to 200 grams per square metre was irradiated for 150 minutes, each, on both sides with UV light at a wavelength of 365 nanometres and an intensity of 4.5 milliwatts per square centimetre. After further drying and cutting, the irradiated cast leaf sample and a non-irradiated control were analysed for NNK, NNN, and nicotine content by mass spectroscopy. As compared to the control, the irradiated sample indicated no effect on nicotine content, a reduction of 12 percent in NNK content, and a reduction of 26 percent in NNN content. 

1.-14. (canceled)
 15. A method for reducing an amount of at least one tobacco-specific nitrosamine in an aerosol-generating substrate, the method comprising: providing a tobacco slurry containing the at least one tobacco-specific nitrosamine; irradiating the tobacco slurry with ultraviolet light; and drying the tobacco slurry to form the aerosol-generating substrate.
 16. The method according to claim 15, further comprising casting the tobacco slurry before the drying of the tobacco slurry, wherein the casting the tobacco slurry is performed before or after the irradiating of the tobacco slurry.
 17. The method according to claim 15, wherein the ultraviolet light irradiance of the tobacco slurry is at least 4 milliwatts per square centimeter.
 18. The method according to claim 15, wherein the tobacco slurry is irradiated with the ultraviolet light for less than 60 minutes.
 19. The method according to claim 15, wherein the ultraviolet light has a peak intensity at a wavelength of between 315 nanometers and 400 nanometers.
 20. The method according to claim 15, wherein the ultraviolet light has a peak intensity at a wavelength of between 350 nanometers and 380 nanometers. 